Cylindrical rolls are utilized in a number of industrial applications, especially those relating to papermaking. Such rolls are typically employed in demanding environments in which they can be exposed to high dynamic loads and temperatures and aggressive or corrosive chemicals. As an example, in a typical paper mill, rolls are used not only for transporting a fibrous web sheet between processing stations, but also, in the case of pressure and calender rolls, for processing the web sheet itself into paper.
Typically rolls used in papermaking are constructed with the location within the papermaking machine in mind, as rolls residing in different positions within the papermaking machines are required to perform different functions. Because papermaking rolls can have many different performance demands, and because replacing an entire metallic roll can be quite expensive, many papermaking rolls include a polymeric cover that surrounds the circumferential surface of a metallic core. By varying the polymer or elastomer employed as a cover, the cover designer can provide the roll with different performance characteristics as the papermaking application demands. Also, replacement of a cover over a metallic roll can be less expensive than the replacement of an entire metallic roll.
It is particularly prevelant to employ elastomers in covers for papermaking rolls, such as natural rubber or synthetic elastomers such as neoprene, styrene-butadiene (SBR), nitrile, chlorosulfonated polyethylene (also known under the name hypalon), and EDPM (the name given to an ethylene-propylene terpolymer formed of ethylene-propylene diene monomer). Because elastomers are typically versatile materials, elastomeric covers can be used in a variety of papermaking applications. For example, rubber covers may be used in smoothing press rolls employed in the press section of a papermaking machine, or may also be employed in the dryer section of a papermaking machine in size press rolls (where starch is added to paper stock) and in breaker stack press rolls (in which non-uniformities in the paper are flattened or removed).
Typically, elastomeric covers employed in papermaking machines have the requisite strength, elastic modulus, and resistance to elevated temperature, water and harsh chemicals to withstand the papermaking environment. In addition, rubber covers employed in the aforementioned areas are designed to have a predetermined surface hardness that is appropriate for the process they are to perform, and they typically require that the paper sheet "release" from the cover without damage to the paper sheet. Also, in order to be economical, the cover should be abrasion- and wear-resistant. Designers of covers generally attempt to achieve this balance of properties by using different base rubber compounds and by including different fillers and additives in the compound. However, often the inclusion of a filler or additive to satisfy one desired property can adversely impact another. As an example, the "releasability" of the cover may be negatively affected by the inclusion of a fibrous filler added to increase strength and hardness. As such, designers of roll cover compounds are constantly searching for new compounds to satisfy the myriad of application demands presented by papermakers.